The present invention relates to a magnetic recording and reproducing apparatus for digital video signals and more particularly to a video signal recording and reproducing apparatus having exchangeability with the existing analog VTR.
Currently, an analog type VTR using an oxide tape of xc2xd-inch width has been practiced as a domestic video signal recording and reproducing apparatus.
On the other hand, practicing of digital broadcasting expected to be next-generation TV broadcasting has been promoted. For example, in the United States, an ATV (Advanced Television) scheme is known in which a wide-band video signal having higher resolution than a video signal (hereinafter referred to as an SD (Standard Definition) signal) in the existing NTSC scheme or PAL scheme is subjected to high-efficiency digital compression coding and is broadcast at a bandwidth of 6 MHz which is the same as that in the existing TV broadcasting. Also, a system has been known in which the SD video signal is subjected to high-efficient digital compression coding by using an MPEG (Moving Picture Experts Group) system and is broadcast through a satellite or a coaxial cable.
The digital broadcasting systems as above are detailed in The Journal of the Institute of Television Engineers of Japan, Vol.47, No.4(1993), pp.486-503.
Conceivably, the digital TV broadcasting will be put into practice in the near future and will be practiced in a coexistent form with the analog TV broadcasting but the conventional analog VTR has failed to record and reproduce a digital video signal while keeping the digital signal intact.
An object of the present invention is to provide a video signal recording apparatus and a video signal recording and reproducing apparatus which have exchangeability with the existing analog VTR and which can record and reproduce a video and audio signal used in, for example, the digital TV broadcasting and subject to digital compression coding while keeping the digital signal intact.
To accomplish the above object, according to the present invention, in a video signal recording and reproducing apparatus having a first magnetic head group for recording and reproducing an analog video signal on and from a video track, a second magnetic head group for recording and reproducing an analog audio signal on and from a depth layer underlying the video track, and a servo circuit for controlling the rotation of a drum and the travel of a tape, there are provided digital recording signal processing means for performing formatting and channel coding (modulation) of a digital video signal, analog/digital selecting means for selecting an analog video signal or a digital video signal for a signal to be recorded, analog/digital discriminating means for determining the recorded signal as to whether to be an analog video signal or a digital video signal, and digital signal processing means for demodulating a reproduced digital video signal and performing the de-formatting processing such as error correction, whereby metal heads of a narrow gap are used for the second magnetic head group and recording and reproduction of the digital video signal is effected by means of the second magnetic head group.
In the video signal recording and reproducing apparatus according to the present invention, there are further provided a third magnetic head group being dedicated to recording and reproduction of a digital video signal at a transmission bit rate of the digital video signal, and means for recording and reproducing an identification signal for discriminating between analog and digital.
In the case of analog recording, an audio signal is recorded by means of the second magnetic head group. At that time, since metal heads are used for the second magnetic head group, recording reaching a depth of a magnetic layer even in the presence of the narrow gap can be permitted and the sufficient reproducing performance can be ensured even when overwrite recording of an analog video signal is effected on a surface layer.
On the other hand, a digital video signal is added with, for example, an error correction code, formulated into blocks and subjected to channel coding (modulation) by means of the digital recording signal processing means and recorded, by means of the second magnetic head group or the second and third magnetic head groups, on a helical track formed in an oblique direction of the magnetic tape. At that time, through the processing on time domain in the digital recording signal processing means, the input digital video signal can be recorded at a substantially constant recording bit rate regardless of a transmission bit rate of the input digital video signal. The servo circuit causes the rotary drum to rotate at a substantially constant rotation speed corresponding to the recording bit rate and controls the transportation speed of the magnetic tape by switching it in accordance with the transmission bit rate of the inputted digital video signal. An identification signal indicating that the recorded signal is the digital video signal is recorded on a so-called linear track in the longitudinal direction of the magnetic tape.
During reproduction, the analog/digital discriminating means detects the identification signal recorded on the linear track and determines the recorded signal as to whether to be an analog video signal or a digital video signal. Then, the reproduced digital video signal is subjected to the processing such as demodulation and error correction by means of the digital reproduced signal processing means, so that the original digital video signal is restored. At that time, since the heads of a narrow gap are used for the second magnetic head group, short-wavelength recording complying with the gap length can be permitted and as a result, recording and reproduction of digital video of high picture quality can be realized.